Internal combustion engine



May 5, 1935 H. c. EDWARDS 2,039,525

RY L C MBUST N Patented May 5, 1936 PATENT DFFICE INTERNAL COMBUSTION ENGINE Herbert C. Edwards, Detroit, Mich., assignor to Packard Motor Car Company, Detroit, Mich., a corporation of Michigan! Application May 14, 1934, Serial No. 725,477

13 Claims.

This invention relates to'internal combustion engines and more particularly to glow plugs.

In order 'to assist in starting compressionignition engines using air and fuel oil as the fuel charge, it has been found advantageous to employ some form of heating means to assist combustion. Itis conventional practice to provide the combustion chambers of such engines with glow plugs which consist of a body, an electrode insulated from the body and connected with a source of electric supply, and a' bare resistance wire secured at its ends to the body and electrode. Considerable diiiiculty has been encountered in developing glow plugs capable of withstanding the heat, vibration and forces to which they are subjected in the combustion chambers of compression-ignition engines, and particularly when such engines are designed to operate at high speeds. The main difficulty has been found to reside in wire failure due to fatigue at the end connections and burning out intermediate the ends because of shorting contact with the electrode. Relatively large diameter wire has sufficient body so that it is generally self` sustaining to an extent such that the vibration and the force of turbulence, compression and explosion in the combustion chamber will not move it into shorting contact with the electrode. Some wire has characteristics or is of such small diameter that it is not self sustaining and, under such circumstances, it must be supported intermediate its ends in an insulated relation with the electrode. It has been4 proposed to apply formed sleeves of insulating material on the electrode and to provide wire rey ceiving recess means on the periphery of thesleeves, but it has been my experience that such sleeves expand and contract differently than the electrode and this, together with `the vibration, heat and forces in the combustion chambers combine in soon cracking the sleeves so that they disintegrate. lSuch disintegration allows the wire to contact with the electrode and the sleeve chips to score the pistons and cylinders and otherwise cause disastrous results to other engine parts'.

An object of my invention is to provide glow plugs which will withstand long usage in'high speed engines of the compression-ignition type. Another object of the invention is Yto provide a glow plug having high resistance wire associated with an electrode in a manner such that it will function properly for a long period of use in a high speed compression-ignition engine.

Afurther object of the invention is to provide a new and novel form of electrode for glow plugs.

(Cl. 12S-145) Still another object of the invention is to provvide a glow plug in which the electrode, on which a resistance wire is wound, is coated with a heat resisting material having qualities suc d) that the contraction and expansion will be similar to that of the electrode.

Other objects of the invention will appear from the following description taken in connection with the drawing, which forms a part of this specification, and in which:

Fig. 1 is a side elevational view of a glow plug which incorporates my invention enlarged several times its normal size;

Fig. 2 is a longitudinal sectional View of the same.

Referring now to the drawing by characters of reference, I Il indicates the glow plug body which is provided with a knurled flange II at one end and a threaded periphery I2 at the other and the other end projecting past the body end I2 and threaded as indicated at Il.

The portion of the electrode within the body is similar in cross section to the body bore but is of slightly less diameter so that an insulator sleeve I8, preferably formed of mica, can be interposed therebetween. A ring abutment member I9, formedof insulation material such as mica, surrounds the threaded end I6 of the electrode and engages an end of the body, such element, serving to locate the mica sleeve. Surrounding the threaded end I6 of the electrode and engaging the abutment member isl a washerl 2li and a nut 2I is screwed on this end of the electrode and serves to secure the previously described elements in a definite relation. It will be seen that, as thenut is turned on the shaft toward the body, it will wedge the body and the electrode together. An electric cable 22 leads from -a source of electric supply and is provided Aat its end with a contact clip 23 which is telescoped on the threaded end I6 of the electrode.

The clip bis held against the nut 2l by a nut 2l 1- which is screwed on the electrode. l

The glow plug resistance wire is indicated at 25, one'end 26 of the wire beingprojected into an plastic quality so that the layer. of porce opening Il in the threaded end of the glow plug body and suitably retained therewith by peening a portion of the body as indicated at 21. The other end 2l of the resistance wire is secured to the end of the electrode projecting past the threaded end of the body. In the present instance, a' groove' 28 is formed to extend substantially radially in the end of the electrode and terminates in a recess as indicated at 3l. The wire end 2t projects into the recess III and is bent to lie in the groove 29. Thefintermediate portion of the resistance wire is coiled around the electrode as will be hereinafter described.

The resistance wire illustrated in the drawing is of anch small cross section that it is incapable of sustaining itself against the vibration, heat and forces developed within the combustion chamber, into which it projects, without quickly becoming fatigued to an extent soon resulting in breakage or burning. I have found therefore, that, with a heating wire of this type, it is necessary to provide asupport for it and in the presentinvention I have utilized the central electrode for this purpose. In so supporting the Yheating wire I have provided a heat resisting insulation material between the wire and the electrode.

It is the purpose of this invention to provide av heat resisting insulation material between the `electrode and the coil of the resistance wire which will be of a character such that it will expand and contract with the electrode and. at the same time, serve as a mandrel on which the :wire' can be tightly wound in orderto serve as both a support for the wireand means for retaining it in va. predetermined coiled relation.

As above set forth, vthe electrode is formed with a 'peripheral recess in the form of a thread I1 which extends helically. I propose to coat the threaded portion oi the electrode with an insulationmaterial having a high heatresistance and characteristics such that it will expand and contract in substantially the same manner as the electrode. To this end, I propo to employ a vitreous material in the form of porcelain enamel which is applied so that it forms a thin -coating on the threaded portion of electrode as indicated at Il in the drawing.

The porcelain enamel can be .formed of materials in the following proportion: 400 pounds of frit, 20 pounds of clay, and 12 pounds of black oxide. To this-mixture is added 140 pounds of water and the entire mass is then mixed in a porcelain lined mill until it is of fine mesh. Such mixture is then preferably allowed to s'tand for a week during which time there is a chemical reaction between the clay 'and the frit. 'I'he excess water rises to the top of the mixture, after it stands, leaving a relatively thick substance therebelow and such excess water is removed and the remaining substance is placed in a tank or a spray for the purpose of either dipping or spraying the threaded portion of the electrode so that -a coating of material will be placed thereon. 'I'he electrode v'so coated is then dried at a' temperature of about 200 Fahrenheit and then put in an oven and fused, at a temperature of about 1420 Fahrenheit, for a period of ten to twentyve minutes. I have found that the clay provi es a on the electrode will readily expand and contrae in the same proportion as the electrode -without cracking. y

The wire is wound tightly against in the thread recess oi' the electrode endsthat glow plugs of such character will withstand many hours of operation without the porcelain cracking and without the wire becoming fatigued.

Although the invention has beenv describedvin connectiony with a specific embodiment, the principles involved are susceptible of numerous other applications which will readily occur to persons skilled in the art. The invention is therefore to be limited only as indicated by the scope of the appended claims.

WhatI claim is:

1. A glow plug for internal combustion engines comprising a body. an electrode insulated from and carried by the body, a thin coating of porcelain on one end of the electrode, and a re sistance wire secured at its ends to the body and the electrode respectively, an intermediate portion of the wire being coiled against the porcelain coating on the electrode.

2. A glow plug for internal combustion engines comprising a body. an electrode insulated from and carried by the body, an end of the electrode projecting beyond an end of the body being peripherally recessed, a coating of porcelain on the recessed projecting end oi' the electrode, and a resistance wire wound tightly against the porcelain coating in the recessed portion of the body and secured at its .ends to the body and the electrode respectively.

3. An electrode for glow plugs comprising a body formed of metal, peripheral threads on one end of the' body, and a porcelain coating on the threaded surface of the body.

4. An electrode for glow plugs comprising an elongated metal body having threads formed around 'a portion thereof.

5. An electrode for glow plugs comprising `a metal body having theperiphery of` one end formed with a helical recess, and a porcelain coating baked on the recessed end of thebody.

6. A glow plug for internal combustion engines comprising a body.' an electrode insulated from and carried by the bocLv, said electrode having a peripheral helical recess in a portion thereof, a thin porcelain lcoating over the recessed portion of the electrode, and a resistance wire wound in the recess in engagement with the porcelain, one end of the wire being attached to the electrode and the other end of. the wire being attached to the body. r

7. An electrode for glow plugs comprising a metal body having a peripheral wire receiving groove in a portion thereof, and a porcelain enamel coating formed on the grooved portion of said body.

,8. An electrode for glow plugs comprising a metal body having a spiral thread on the pe. riphery of im portion thereof, and an insulva tion coating applied izo the threaded portion of said body.

9. An' electrode for glow plugs comprising a body having a peripheral recess around a portion' thereof, and insulation means applied to and baked on the body to cover the recess surfaces.

10. An electrode for glow plugs comprising a body having wire retaining means formed therein, and an insulation coating baked on the portion of body having the wire retaining means therein, said coating being formed of material having a plastic quality when subjected to heat.

11. In a glow plug, inner and outer metallic members having small openings of uniform diameter extending upwardly from their lower ends, one of said members projecting beyond the other and carrying in its projecting portion a helical groove extending from adjacent the opening in the lower' end of one member to adjacent the opening in the lower end of the other member, a.

glow wire having its opposite end portions extending upwardly and completely enclosed by and lling said openings, and its exposed intermediate portion seated in said groove, and an adherent coating 'of non-conducting material on said grooved projection.

12. An electrode for glow plugs comprising a metal body having a portion of the periphery formed with a wire receiving recess, and a coating formed on the recessed portion of said body, said coating having heat resisting and insulating characteristics.

13. An electrode for glow plugs comprising a 

